The present application claims priority to Japanese Application(s) No(s). P2000-276552 filed Sep. 12, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a new manufacturing method for a print head. More specifically, the present invention relates to a technique for reducing displacements as much as possible between ink-pressurizing cells, which are individually provided with heating elements, and ink-ejection nozzles, which individually correspond to the ink-pressurizing cells.
2. Description of the Related Art
Conventionally, such print heads are known in which ink-pressurizing cells, which are individually provided with heating elements, are covered by a nozzle-formed member, in which small ink-ejection nozzles are formed. When the heating elements are rabidly heated, bubbles of ink vapor (ink bubbles) are generated, and ink drops are ejected from the ink-ejection nozzles due to pressures applied by the ink bubbles.
Such a print head normally has a construction shown in FIGS. 11 and 12. With reference to the figures, a print head a includes a substrate member d which is provided with heating elements c and which defines side surfaces and one end surface of ink-pressurizing cells b. The substrate member d is constructed by depositing the heating elements c on a surface of a semiconductor substrate e formed of silicon, etc., and laminating a barrier layer f on the semiconductor substrate e at the same side as the side at which the heating elements c are deposited. The barrier layer f defines side surfaces of the ink-pressurizing cells b; in other words, it serves a side walls of the ink-pressurizing cells b. The barrier layer f is formed of, for example, a dry film which is curable by light exposure, and is constructed by laminating the dry film over the entire surface of the semiconductor substrate e, on which the heating elements are formed, and removing unnecessary parts by a photolithography process. Accordingly the substrate member d is completed.
Then, a nozzle-formed member g is laminated on the barrier layer f of the substrate member d. The nozzle-formed member g is formed of, for example, nickel, by using the electroforming technique. The nozzle-formed member g is provided with ink-ejection nozzles h, which are aligned relative to the heating elements c deposited on the substrate member d.
Accordingly, the ink-pressurizing cells b, of which end surfaces are defined by the substrate member d and the nozzle-formed member g, and side surfaces are defined by the barrier layer f, are formed. The ink-pressurizing cells b are linked with an ink passage i, and are provided with the ink-ejection nozzles h which oppose the heating elements c. The heating elements c in the ink-pressurizing cells b are electrically connected to an external circuit via conductors (not shown) deposited on the semiconductor substrate e.
Normally, a single print heat includes hundreds of heating elements c and ink-pressurizing cells b containing the heating elements c. The heating elements c are selectively heated in accordance with a command issued by a control unit of a printer, and ink drops are ejected from the corresponding ink-ejection nozzles h.
In the print head a, the ink-pressurizing cells b are filled with ink supplied via the ink passage i from an ink tank (not shown) which is combined with the print head a. When a current pulse is applied to one of the heating elements c for a short time such as 1 to 3 xcexcs, the heating element c is rapidly heated, and a bubble of ink vapor (ink bubble) is generated at the surface thereof. Then, as the ink bubble expands, a certain volume of ink is pushed ahead, and the same volume of ink is ejected out from the corresponding ink-ejection nozzle h as an ink drop. The ink drop, which is ejected from the ink-ejection nozzle h, adheres (lands on) to a print medium such as a piece of paper, etc.
In the above-described print head a, characteristics of ink drop ejection are affected by positional relationships between the heating elements c and in-ejection nozzles h, and between the ink-pressurizing cells b and the ink-ejection nozzles h. When displacements between the heating elements c and the ink-ejection nozzles h, and between the ink-pressurizing cells b and the ink-ejection nozzles h, are large, the ejection speed may be reduced and the ejecting direction may be changed. Furthermore, it may even be impossible to eject ink drops. Accordingly, displacements between the heating elements c and ink-ejection nozzles h, and between the ink-pressurizing cells b and the ink-ejection nozzles h, lead to a degradation of the printing quality, and thus are a large problem.
Generally, heating processes are necessary for manufacturing the print head a. For example, after the barrier layer f is formed on the semiconductor substrate e and the nozzle-formed member g is laminated on the barrier layer f, a heat curing process for curing the barrier layer f and fixing the nozzle-formed member g is performed at a high temperature. In addition, another high-temperature curing process is performed to provide ink resistance to the barrier layer f, which is formed of dry film resist.
As described above, heating processes are necessary for manufacturing a print head. Coefficients of linear expansion of silicon, which is normally used for forming the semiconductor substrate e, and nickel, which is normally used for forming the nozzle-formed member g, differ by approximately one order of magnitude.
When two materials having extremely different coefficients of linear expansion are laminated together in a heating process, relative displacement occurs due to the difference in shrinkage rates. Such a displacement varies in accordance with the difference in the coefficients of linear expansion between the members that are laminated together, and is increased as the difference becomes larger.
With reference to FIG. 13, at position (a), the heating element c and the ink-ejection nozzle h, and the ink-pressurizing cell b and the ink-ejection nozzle h, are aligned. However, at position (b), which is apart from position (a), the ink-ejection nozzle h is displaced relative to the heating element c and to the ink-pressurizing cell b. Furthermore, at position (c), which is farther apart from position (a), the ink-ejection nozzle h is completely displaced from the ink-pressurizing cell b. Such a displacement increases along with the size of the members which are laminated together. When the heating element c and the ink-ejection nozzle h are displaced relative to each other (see FIG. 13, position (b)), the ejection direction is changed. In addition, when the displacement is increased still further (see FIG. 13, position (c)), it becomes impossible to eject ink.
In the printer market, it is required to increase the printing speed, and one approach to satisfy this requirement is to increase the number of nozzles from which ink is ejected. When the resolution of a printer is maintained and the number of nozzles is increased, the size of a print head is also increased. Thus, the influence of the displacements between the heating elements c and the ink-ejection nozzles h, and between the ink-pressurizing cells b and the ink-ejection nozzles h, which occur due to the difference in coefficients of linear expansion, is also increased. In addition, in large print heads such as line heads, etc., there is a large problem in that the displacements between the heating elements c and the ink-ejection nozzles h, and between the ink-pressurizing cells b and the ink-ejection nozzles h, become relatively large.
Accordingly, an object of the present invention is to reduce the displacements as much as possible between the ink-pressurizing cells, which are individually provided with heating elements, and the ink-ejection nozzles, which individually correspond to the ink-pressurizing cells.
In order to achieve this object, according to the present invention, a manufacturing method for a print head includes the step of laminating a correcting member, which has approximately the same coefficient of linear expansion as the substrate member, to the nozzle-formed member, so that the nozzle-formed member expands and shrinks in accordance with the coefficient of linear expansion of the substrate member when the temperature varies,
wherein a nozzle interval L1 of a nozzle-formed member which doesn""t laminate a correcting member, which is an interval between the ink-ejection nozzles, at an operating temperature T0, at which the print head is used, is determined according to the following equation:
L1=L2(1+xcex12xcex94T)/(1+xcex11xcex94T)
wherein:
L2: nozzle interval and heater interval, which is an interval between the ink-pressurizing cells and between the heating elements, at the operating temperature after the print head is completed
xcex11: coefficient of linear expansion of the nozzle-formed member
xcex12: coefficient of linear expansion of the correcting member, which is approximately the same as the coefficient of linear expansion of the substrate member
T1: laminating temperature of the nozzle-formed member and the correcting member
xcex94T: difference between the laminating temperature T1 and the operating temperature To (xcex94T=T1xe2x88x92To).
Thus, in the print head of the present invention, the nozzle-formed member is supported by the correcting member, and the interval between the ink-ejection nozzles formed in the nozzle-formed member extends and shrinks along with a head frame. Since the coefficient of linear expansion of the correcting member is approximately the same as that of the substrate member, the displacements between the heating elements and the ink-ejection nozzles, and between the ink-pressurizing cells and the ink-ejection nozzles, can be made zero, or can be reduced to an extremely small amount.
Furthermore, since the interval between the ink-ejection nozzles L1 is determined according to the following equation:
L1=L2(1+xcex12xcex94T)/(1+xcex11xcex94T),
the nozzle interval and the heater interval can be made approximately the same after the nozzle-formed member and the correction member are laminated together.